Are Birds Mammals?

Some of you may not know that other people are confused about the difference or similarities between birds and mammals, and most often than not, they conclude that birds are classified as mammals. 

In this blog, we’re going to answer the question that some people are often confused about and this is “Are Birds Mammals?”. 

Here’s Why Birds Are NOT Mammals

Birds aren’t mammals for these specific reasons:

  • Birds belong to the Aves class. The Aves class has animals under it that share common characteristics that make birds birds
  • Mammals belong to the Mammalia class. In order to be classified as a mammal, the animal must share the characteristics of one. 
  • Two of these classes are different, hence they’re separate classes in the Animal Kingdom. 

This is a concise explanation to answer the question of whether birds are mammals or not, but I will further elaborate as to why it is so. 

Animal Kingdom Classification

Think of the animal kingdom as a chart made by scientists, and this chart is divided into groups. Refer to these groups as ‘animal classifications’. The two main classes we’ll be focusing on are the Aves and Mammalia. Within a class, animals are sorted into groups. The animals grouped together in the same family are closely related. 

Scientists base on the physical characteristics of animals when it comes to sorting them into their respective classes or family. There are characteristics that animals share in the Aves class that classifies them as birds and the same goes for those animals that share similar characteristics in the Mammalia class. 

That just proves that birds are not mammals. The two classes (Aves and Mammalia) are different and that’s as simple as it gets. But there can be some confusion between birds and mammals because they both share some similarities and that gives birth to misconceptions from people. 

Differences Between a Bird and a Mammal

Both mammals and birds may share a few similar characteristics, we’ll be discussing how different they actually are to each other:

Characteristics of a Bird

  • Feathers. In the entire animal kingdom, only birds are covered with feathers. There are two types of feathers for various kinds of birds, one is called the contour feathers and the other is down feathers. Contour feathers are lightweight but strong and these give a bird its coloring and smooth form. 

These type of feathers are also the ones that help birds fly. It helps the birds steer and not spiral out of control when they’re in the sky. Down feathers on the other hand serve as an insulating layer in a birds skin and it also covers the bodies of young birds. This is why ducks can survive floating around in ice-cold ponds. 

  • Beaks and absence of teeth. If you’ve ever watched a documentary on birds, you may have probably seen how the mother bird (or sometimes the father) digest the food first before feeding it to her babies. This is because birds don’t have teeth and young birds can’t eat food by themselves yet and need help from their mother. 

Birds cut up the food into little pieces with their beaks before digesting it. And all beaks are often specialized according to its diet. 

  • Egg-laying. Birds lay hard eggs. While there are mammals that also lay eggs, (which are called monotremes) these eggs have much softer shells. 
  • Respiratory system. Birds don’t have the same lungs the way mammals do. They don’t have a simple respiratory system with two lungs neatly tucked inside of their chest. Their lungs make up most of their bodies. Birds have air sacs in their lungs and the air that they inhale only flow in one direction all the time. 

This enhances their ability to to constantly channel air in their lungs and it’s more efficient than what mammals have. 

Characteristics of a Mammal 

  • Hair. If an animal has hair then best believe it falls under class Mammalia! All adult mammals have hair and they may either be covered entirely in it or it may be located in certain parts of their bodies like the area around their mouth. Did you know that fur traps in air and keeps these mammals warm? 

Hair serves a lot of purpose besides keeping them warm, for example, the whiskers in animals help them get a good sense of their environment. Then there are other animals like the whale, these mammals have little to no hair and make use of their blubber to keep them warm. 

Porcupines and hedgehogs have quills and these are specialized hairs that keep them protected against predators. 

  • Give birth to live young. Mammals give birth to live young, apart from those monotreme species that lay eggs. 
  • Skin and glands. A mammal is covered with a skin and this skin is an organ that produces hair and in other particular species, these produce horns, claws, hooves, or nails. Skin also has various kinds of glands. You may have heard of the mammary glands and this gland is found in all mammals. 

The mammary glands in female mammals help them in feeding their young with milk. Oil glands help lubricate their hair and skin. Sweat glands that are present in some species help them eliminate waste and keep them cool. Then there are also scent glands in many mammals and these help attract mates, mark territories, and act as a form of defense. 

  • Teeth. All mammals have specialized teeth and these have a lot to do with their diet. Scientists are able to determine a certain mammal’s diet just by looking at their teeth. The teeth have four parts, there are incisors which are the front teeth, next to it are the canine teeth, then the premolars and molars at the back. Humans have all four. 

Since humans have all four of these teeth, they are classified as omnivores. Carnivores have larger canine teeth for gripping and tearing muscle apart. Herbivores have large premolars and molars to get through tough fibers in plants. 

  • Feeding their young with milk. Only mammals have the capacity to produce milk and feed their young with it. 

Similarities Between a Bird and a Mammal 

Despite being very different animals from each other, they do share some similar characteristics:


Both birds and mammals can maintain a constant body temperature and have no need of any other external source for heat. This characteristic that both classes share have a requirement wherein they must have a certain calorie intake and have a particular weight in order to maintain the ability to keep themselves warm and active in cold temperatures. 

Cold-blooded animals like reptiles don’t need to eat that much food but that also means they can’t thrive in cold temperatures like mammals and birds can. With that being said, warm-blooded animals have the ability to live in any landmass on Earth. 


Both mammals and birds have skeletal systems, of course that means they have backbones and that makes them vertebrates. But the thing is, birds have hollow bones and these are lightweight which in turn, makes things easier for birds when they fly. 

The structural matrix of their bones add strength that is strong enough to withstand the pressure of taking off into the skies and landing. 


Birds make it look so easy when they fly but in reality, flying is an exhausting thing to do and requires a lot of energy from birds. This is why birds have evolved into having four-chambered hearts which are already present in mammals. This type of circulatory system allows the birds to separately pump oxygenated and deoxygenated blood. 


The blood of both the birds and mammals contain red and white blood cells. These are called the erythrocytes and leukocytes. The red blood cells are responsible for distributing oxygen and give the blood its red color. 

Caring for Young 

Both the mammals and birds share the similarity of taking care of their young. Although, it does depend on the type of species when it comes to the duration of how long they’ll be taking care of their young. Birds feed their young by using their beaks and mammals feed their young by giving them their nutritious milk. 

Flight is NOT a Characteristic for Being a Bird 

If an animal can fly, that doesn’t mean they automatically identify as birds. Flight is not a distinct characteristic that defines birds and that’s because there are other animals that can fly but they are necessarily birds. For instance, a bat can fly and they’re mammals. Then there are reptiles and amphibians that can glide (although gliding is different from flying altogether). 

Another reason as to why flight is not a determiner that makes birds birds is the existence of flightless birds like the Penguins, Ostriches, and Kiwis. They had ancestors who could fly dating back centuries ago but due to evolution their bodies have adapted and changed. 


In this blog, we’ve answered the question that some people are often confused about and this is “Are Birds Mammals?”. In short, they aren’t. Birds are completely different animals and that in itself is enough proof that they are indeed not mammals. Plus, the overall structure of animals belonging to the Aves class and Mammalia class are different from one another. 

Mammals have four limbs and a tail wagging around while birds have beaks and feathers. 

They’re two separate things. Mammals are mammals and birds are birds. 

FAQ’s: Are Birds Mammals?

Are birds mammals yes or no?

No. Birds are definitely NOT mammals. Birds are birds and mammals are mammals. The birds belong to class Aves which is a separate class from Mammalia. 

What is a bird classified as?

Birds are classified under class Aves according to Linnaean taxonomy. Interestingly enough, in Phylogenetic taxonomy, class Aves is placed in the dinosaur clade Theropoda. 

Are birds classified as animals?

Animals are spread in all kinds of environments. Whether it’d be from the marine or terrestrial environments, all insects, fish, and birds are animals. 

What is considered a mammal?

An animal is considered a mammal if they have fur, are born alive, warm-blooded, and are fed by lactating mothers with their milk thanks to a mammal’s mammary glands. Mammals have the most complex brains out of all the other animals that belong to their own respective classes. 

What animal is not a mammal?

Animals like reptiles, birds, and fish are not mammals. Animals that have backbones are referred to as Vertebrates. Those who belong to the category of Vertebrates are Mammals, reptiles, birds, and fish. These animals all have backbones. 


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